The present invention relates to a magnetic thim film and more particularly to such film including iron oxide as a principal component, and method of making it.
The magnetic thin film is used, for example, as the permanent magnet for biasing the magnetoresistive element of magnetoresistive transducers or as magnetic recording media such as magnetic discs, magnetic tapes, etc.
The requirements of magnetic thin film for biasing the magnetoresistive (hereinafter referred to as MR) element in an MR head are as follows:
To improve an adequate biasing magnetic field, a large residual magnetic flux density B.sub.r is required. If as the MR element, for example, a Permalloy film of 83% Ni-17% Fe being uniaxially anisotropic and having a saturation magnetic flux density Bs of 10.sup.4 G, is used and formed to a thickness of t.sub.mr .mu.m on a non-magnetic substrate of silicon, glass, alumina, etc., the product of the thickness t.sub.b .mu.m and the residual magnetic flux density B.sub.r of the magnetic thin film should meet the following condition: EQU B.sub.r .multidot.t.sub.b &gt;10.sup.4 t.sub.mr [G.multidot..mu.m](I)
If the substrate is of a soft magnetic material such as ferrite, Sendust, Permalloy, etc., roughly the following condition is required in place of (I): EQU B.sub.r .multidot.t.sub.b &gt;2.times.10.sup.4 t.sub.mr [G.multidot..mu.m](II)
To prevent the demagnetization by the recording media such as magnetic tape, the magnetic thin film is required to have high coercive force. If as the recording media, for example, .gamma.-Fe.sub.2 O.sub.3 base magnetic tape is used, the coercive force H.sub.c of the magnetic thin film should meet the following condition: EQU H.sub.c &gt;500Oe (III)
If a metal alloy tape with the coercive force of 2,000 Oe are used as the recording media, the following condition is required place of (III): EQU H.sub.c &gt;2,000Oe (IV)
Besides the above-mentioned properties, the large specific resistance is also required. Further the surface of the magnetic thin film should be flat, having no cracks or recesses. If the film has such a defective surface, the surface of the MR element formed on the film will also have such cracks or recesses, giving rise to formation of many magnetic segments in the MR element, causing Barkhausen noise in the output signal of the MR head.
When the magnetic this film is used as the recording medium such as magnetic disc, magnetic tape, etc. in digital recording at about 10,000 to 20,000 B.P.I., for example, H.sub.c should be around 500 Oe, and B.sub.r t.sub.b, around 1,000 G.multidot..mu.m (therefore if the film thickness is 0.5 .mu.m, B.sub.r should be 2,000 G, for example).
Hithereto known magnetic thin films available for above-mentioned usages are principally iron oxide base films. However they could not sufficiently satisfy the above-mentioned condition, particularly the very high coercive force.
As for the method of manufacturing the oxide magnetic film film, of the many methods available, the reactive evaporation process is most popular because of its advantage in that manufacturing is possible at relatively low temperature, and it needs a small number of manufacturing steps. However such method involves a troublesome step such as having to anneal the thin film formed by vapor deposition in air for a long time i.e. more than 10 hours. And it is also disadvantageous that during such long time annealing, dust in the air or dirt is deposited on the film, badly affecting subsequent lamination of other films.